Full color organic electroluminescent (EL), also known as organic light-emitting devices (OLED), have been demonstrated recently as a new type of flat panel display. OLED devices are attractive because of their low driving voltage, high luminance, wide-angle viewing, and capability for full color flat emission displays. In simplest form, an organic EL device is comprised of an anode for hole injection, a cathode for electron injection, and an organic EL medium sandwiched between these electrodes to support charge recombination that yields emission of light. An example of an organic EL device is described in commonly assigned U.S. Pat. No. 4,356,429. Other examples have been described by Tang, et al. in U.S. Pat. Nos. 4,769,292 and 4,885,211. In order to construct a pixilated display device that is useful, for example as a television, computer monitor, cell phone display or digital camera display, individual organic EL elements can be arranged as an array of pixels in a matrix pattern. This matrix of pixels can be electrically driven using either a simple passive matrix or an active matrix driving scheme. In a passive matrix, the organic EL layers are sandwiched between two sets of orthogonal electrodes arranged in rows and columns. An example of a passive-matrix-driven organic EL device is disclosed in commonly assigned U.S. Pat. No. 5,276,380. In an active matrix configuration, each pixel is driven by multiple circuit elements such as transistors, capacitors, and signal lines. Examples of such active matrix organic EL devices are provided in U.S. Pat. No. 5,550,066 (commonly assigned); U.S. Pat. Nos. 6,281,634; and 6,456,013.
Full color OLED devices are also known in the art. Typical full color OLED devices are constructed of three different color pixels that are red, green, and blue in color. Such an arrangement is known as an RGB design. An example of an RGB design is disclosed in U.S. Pat. No. 6,281,634. Full color organic electroluminescent (EL) devices have also recently been described that are constructed of four different color pixels that are red, green, blue, and white. Such an arrangement is known as an RGBW design. An example of an RGBW device is disclosed in commonly assigned U.S. patent application Publication 2002/0186214 A1. In an RGBW device, high efficiency white-emitting pixels are used to display a portion of the digital image content. This results in improved power consumption relative to an RGB constructed of similar OLED materials.
A white-emitting electroluminescent (EL) layer can be used to form a multicolor device. Each pixel is coupled with a color filter element as part of a color filter array (CFA) to achieve a pixilated multicolor display. The organic EL layer is common to all pixels and the final color as perceived by the viewer is dictated by that pixel's corresponding color filter element. Therefore, a multicolor or RGB device can be produced without requiring any patterning of the organic EL layers. An example of a white CFA top-emitting device is shown in U.S. Pat. No. 6,392,340. Other examples of white-light-emitting OLED devices are disclosed in U.S. Pat. No. 5,683,823, JP 07-142169, and U.S. Pat. No. 5,405,709.
Numerous OLEDs with alternative layer structures, including polymeric materials, have been disclosed, and device performance has been improved. For the commercial success of OLEDs, further improvement in devices is needed. Among the key areas that need further improvement are the efficiency and operating stability of the devices. It is also desirable to improve the color gamut obtainable from such devices.